Optimizing soil remediation with multi-functional L-PH hydrogel: Enhancing water retention and heavy metal...

Agricultural soils face severe challenges, including water scarcity and heavy metal contamination. Optimizing soil remediation efficiency while minimizing inputs is essential. This study assessed the water retention and heavy metal adsorption properties of L-PH hydrogel through aqueous experiments. Fourier Transform Infrared (FTIR) and X-ray Photoelectron Spectroscopy (XPS) elucidated the adsorption mechanisms. The results showed that L-PH hydrogel exhibited high water absorption efficiency, with Zn²⁺ removed via electrostatic interactions and cation exchange, and Cd²⁺ and Cu²⁺ adsorbed through coordination complexation. Soil experiments tested water retention and heavy metal leaching under various application methods (M1 = 0-10 cm mixed, M2 = 10-20 cm mixed, T1 = 5-10 cm layered, T2 = 10-15 cm layered) and rates (NL = 0 %, L1 = 0.1 %, L2 = 0.2 %, L3 = 0.5 %). L-PH reduced water infiltration, enhanced soil water retention, and decreased heavy metal mobility across all treatments. The highest water retention was observed in the M1 method. Under M1L1, cumulative leaching of Cd²⁺, Cu²⁺, and Zn²⁺ decreased by 68.84 %, 33.44 %, and 83.60 %, respectively. Two-way ANOVA revealed that application rate had a greater effect on leaching than the method. FTIR and XRD analyses showed that at low concentrations (L1, L2), L-PH formed coordination bonds with Cd²⁺ and Cu²⁺, creating Cd(HCOO)₂·2(NH₂)₂CO and Cu(HCOO)(OH) in the soil. Zn²⁺ was stabilized through adsorption and precipitation, forming Zn(OH)₂, thereby reducing leaching. Higher concentrations of L-PH may have further interacted with Zn, leading to dissolution and adsorption/precipitation processes. Redundancy analysis (RDA) analysis suggests that an increase in organic carbon and moisture content in soil aggregates larger than 2 mm, along with a decrease in bioavailable heavy metals, may enhance heavy metal stabilization, reducing their movement and leaching. This study offers valuable insights into addressing the twin challenges of water scarcity and heavy metal pollution.